Dipolar Cycloaddition Reactions with Quinazolinones: A New Route for the Synthesis of Several Annelated Pyrrolo- and Pyridazinoquinazoline Derivatives

The novel 2-aryl-3a,4,12,12a-tetrahydropyrrolo[3',4':4,3]-pyridazino[6,1-b]-quinazoline-1,3,6-triones (6a–d), 2-aryl-10-oxopyridazino[6,1-b]-quinazoline-3-thio-carboxamides (10a–d) and 2-aryl-3-nitro-1,2,3,4-tetrahydro-pyridazino[6,1-b]quinazolin-10-ones (12a–d) were synthesized via a new, facile one step route involving the reactions of the zwitterion 4, formed in situ, with a variety of N-arylmaleimides 5, 3-aryl-2-cyano-thioacrylamides 8 and ω-nitrostyrenes 11. Dehydrogenation of the tetrahydro derivatives 6a–d and 12a–d in nitrobenzene resulted in the formation of 2-arylpyrrolo[3',4':4,3]-pyridazino[6,1-b]quinazoline-1,3,6-triones (7a–d) and 2-aryl-3-nitropyridazino[6,1-b]quinazolin-10-ones (13a–d), respectively. The structures of the products were confirmed by elemental analysis and spectral data.